1. Field of the Invention
The present invention relates to a socket unit used for tightening a nut while interposing a reaction washer therebetween and to a tightening machine having the socket unit, and more particularly, the present invention relates to a tightening machine having a socket unit, even in a phase misalignment between a nut and a reaction washer, capable of easily fitting an outer socket to a reaction washer in a state where a nut is fitted to an inner socket.
2. Description of Related Art
As shown in FIG. 15, there is a known method in which when structures are to be tightened to each other, a reaction washer 95 is fitted around a bolt 91 projecting from the structure 90, and a nut 93 is tightened from above the reaction washer 95. The reaction washer 95 has a concavo-convex periphery 96 in which twelve V-shaped grooves are repeatedly formed in a peripheral surface of a disk-like washer at about 30° intervals, and the nut 93 is tightened using a tightening machine provided at its tip end with a socket unit while receiving a tightening reaction force by the reaction washer 95.
The tightening machine is concentrically provided with an inner socket holder and an outer socket holder which rotate in opposite directions from each other. The socket unit includes an inner socket and an outer socket which are formed concentrically.
The inner socket is provided at its base end outer periphery with a mounting projection. The mounting projection detachably engages with the inner socket holder of the tightening machine. A mounting groove is formed in an inner periphery of the inner socket holder. The inner socket is fitted to a mounting groove formed in an inner periphery of the inner socket holder without clearance in its circumferential direction. The outer socket also detachably engages with the outer socket holder, and if the tightening machine is operated, the inner socket and the outer socket rotate in opposite directions from each other.
The nut 93 is tightened in such a manner that an inner peripheral surface of a tip end of the inner socket is fitted to the nut 93, and then an inner peripheral surface of a tip end of the outer socket is fitted to the reaction washer 95 and in this state, the tightening machine is operated.
It is necessary to tighten the nut 93 under preset torque, but primary tightening (temporarily tightening) is carried out before a so-called final tightening operation for tightening the nut 93 under the set torque. In this primary tightening operation, positions in the rotation direction (“phase”, hereinafter) of the reaction washer 95 and the nut 93 align with each other in some cases as shown in FIG. 16A, but the phases of the reaction washer 95 and the nut 93 are misaligned in most of cases as shown in FIG. 16B.
When the nut 93 and the reaction washer 95 are compared with each other, the nut 93 is thicker than the reaction washer 95 as shown in FIG. 15. Therefore, when the socket unit is fitted to the nut 93 and the reaction washer 95, the inner socket is firstly fitted to the nut 93, and then, if the socket unit is further moved forward, the outer socket is fitted to the reaction washer 95.
When the inner socket and the nut 93 are fitted to each other, even if the phases of the inner socket and the nut 93 are misaligned each other, if an operator rotates the tightening machine itself around its axis, the phase misalignment can be solved. Therefore, the inner socket can be fitted to the nut 93.
However, when the reaction washer 95 is to be fitted to the outer socket after the nut 93 is fitted to the inner socket, the outer socket does not excellently mesh with the concavo-convex periphery 96 of the reaction washer 95 depending upon the phase misalignment between the reaction washer 95 and the nut 93, as shown in the above and in FIGS. 16A and 16B, and the outer socket cannot be fitted to the reaction washer 95.
Hence, it is proposed that an inner surface shape of a nut-engaging hole 32 formed in the inner socket to which the nut 93 is fitted is not formed into the same hexagonal shape as that of the nut 93, a width of a bottom surface 33a of a groove 33 is widened to about 30° and an inner socket 30 having a nut-engaging hole 32 having clearance is used. Concerning a shape of the groove 33 of the inner socket, see a front view of FIG. 12 of the present invention.
By widening the width of the groove 33, it is possible to provide clearance of about 30° in the case of the illustrated example. Therefore, if a phase misalignment between the reaction washer 95 and the nut 93 is as small as 5° or 10° and is much smaller than 30°, it is theoretically possible to engage the reaction washer 95 with the outer socket if an operator rotates the tightening machine itself around its axis after the nut 93 is made to mesh with the inner socket.
The maximum phase misalignment between the reaction washer and the nut is theoretically 30° but members vary and the nut and the reaction washer are not concentric. Therefore, the maximum phase misalignment between the reaction washer and the nut exceeds 30° in some cases. In such a case, even if the tightening machine itself is rotated, the reaction washer cannot be engaged with the outer socket. Hence, in such a case, a so-called inching operation is required. In the inching operation, the tightening machine is slightly operated to align the phases of the outer socket and the inner socket from each other. If the phases do not align by one inching operation, the inching operation must be repeated many times and this deteriorates operation efficiency.